Sampling two analog pins with an imp001 I don’t understand the results I seem to be getting from the interleaved data. Every so often the two channel values read from the buffer returned by the callback swap position. While pin 1 data readings always start out (when device started) in first pair of bytes, pin 2 in second pair - then, after maybe a few hours, pin 1 data appears in the second byte pair and pin 2 the first. Then a few hours later it may return to the correct sequence, and so on.
Here’s the code that does it:
//sampler buffers
buffer1 <- blob(2000); //2x2 bytes @50Hz gives 10 sec updates
buffer2 <- blob(2000); //double buffer
// Configure analogue pins 1 & 2 to be sampled 50 times per second
hardware.sampler.configure([hardware.pin1,hardware.pin2], 50, [buffer1, buffer2], samplesReady);
//sampler callback every 10 sec...
function samplesReady(buffer, length) {
local ava=0.0;
local avv=0.0;
if (length > 0) {
length/=4; //2 x 16bit samples
for(local i = 0; i < length; i++)
{
ava+=buffer.readn('w');
avv+=buffer.readn('w');
}
ava/=length; //take avg. amps
avv/=length; //take avg. volts
server.log("check: A="+ava+" V="+avv);
} else {
server.error("Overrun");
}
}
Testing with two different fixed voltage levels at the inputs, it’s very obvious that the order is randomly swapping. Am I retrieving the interleaved data correctly by doing two sequential buffer.readn(‘w’) ?
